Eta-expansions in Fω
The use of expansionary η-rewrite rules in typed λ-calculi has become increasingly common in recent years as their advantages over contractive η-rewrite rules have become more apparent. Not only does one obtain simultaneously the decidability of βη-equality and a natural construction of the long βη-normal forms, but rewrite relations using expansions retain key properties when combined with first order rewrite systems, generalise more easily to other type constructors and are supported by a categorical theory of reduction.
However, one area where η-contractions have until now remained the only possibility is in the more powerful type theories of the λ-cube. This paper begins to rectify this situation by considering a higher order polymorphic λ-calculus known as Fω.
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